The present invention generally relates to vehicle braking systems and, more particularly to automobile vehicle controls.
In conventional automotive braking systems, a master cylinder converts a manual application of a force exerted on a brake pedal into a corresponding hydraulic pressure, which is proportioned among the front and rear wheel brakes. In power assisted braking systems, a vacuum booster is interposed between the brake pedal and the master cylinder to increase the amount of fluid pressure transferred through the braking system under the operations of vacuum assistance or hydraulic power.
As an alternative to these conventional automotive braking systems, electro-hydraulic braking systems have been developed to amplify fluid brake pressures using electrically powered boost units. In these systems, the master cylinder pressure is usually coupled through normally open solenoid valves and electrically powered boost units to the wheel brakes. In normal braking, the solenoid valves are activated to isolate the master cylinder from the wheel brakes, and the electrically powered boost units are activated to develop fluid brake pressures based on various braking parameters. In the event of an electrical failure, the solenoid valves may return to their normally open state, re-coupling the master cylinder to the wheel brakes, allowing continued braking with the manually developed master cylinder pressure.
However, the powered boost units of the electro-hydraulic braking systems usually consume considerable power during extended idling when a high level of braking force is not typically required. This condition can occur, for example, when the driver is exerting significant brake pedal force while waiting for a traffic light. In addition to the unnecessary power consumption, this condition typically causes unnecessary heat generation in the powered boost units and controller, possibly adversely affect their durability.
The present invention provides a brake control system for actively controlling the wheel brakes of a motor vehicle. The brake control system includes a closed-loop control system that controls the amount of fluid pressure provided to the wheel brakes. The brake control system provides enhanced brake performance through faster system responses and improved controllability than conventional vacuum-boosted brake systems. The brake control system further decreases power consumption under the certain conditions and improves the durability of the brake system.
One method in accordance with the present invention for providing a command signal to a valve to control fluid pressure to a wheel brake in a braking system includes the steps of determining a pressure signal using a first control technique based on a first set for control gains and a pressure command signal, determining a first current signal based upon the pressure signal, subtracting an actual pressure signal from the pressure command signal to produce an error signal, and determining a second current signal using a second control technique based on the second set of control gains and the error signal. The method further includes subtracting a supply pressure actual signal from a supply pressure nominal signal to produce a pressure differential signal, multiplying the pressure differential signal by a selected gain to produce a third current signal, and summing the first current signal, the second current signal and the third current signal to produce an output signal.
One braking system in accordance with the present invention includes a master cylinder for delivering pressurized fluid in response to a mechanical input. A first sensor provides a supply pressure signal in response to fluid pressure delivered by the accumulator. A second sensor provides a wheel pressure signal in response to fluid pressure applied to at least one wheel brake. A controller is responsive to the wheel pressure signal and supply pressure signal to produce a pressure command signal. The controller implements the steps of determining a first current signal using a first control technique based on a first set for control gains and the pressure command signal, determining an actual pressure signal based upon the wheel pressure signal. subtracting an actual pressure signal from the pressure command signal to produce an error signal, and determining a second current signal using a second control technique based on a second set of control gains and the error signal. The controller also implements the steps of subtracting the supply pressure signal from a supply pressure nominal signal to produce a pressure differential signal, multiplying the pressure differential signal by a selected gain to produce a third current signal, and summing the first current signal, the second current signal and the third current signal to produce an output signal.